11 Acknowledgments

I would like to thank my collaborators and friends A. Barvinsky, G. Dvali, G. ’t Hooft, W. Israel,
V. Frolov, D. Fursaev, R. Mann, R. Myers, S. Mukhanov, D. Nesterov and A. Zelnikov for fruitful
collaboration and many inspiring discussions. I thank G. ’t Hooft, R. Myers and R. Mann for reading this
review and giving valuable remarks. I am indebted to my colleagues N. Mohammedi, L. Villain and,
especially, to S. Nicolis for reading this review and their many comments, which helped to improve the
presentation. As always, the writing of this review would not be possible without the constant support of
my family.